Of course, to you it won't.
Myself, after a year of running official content I'm itching to play a more flexible campaign where the players have some agency to set the difficulty level themselves.
It's as my fighter player said: getting to be Legendary in pole-arms (his chosen specialty) doesn't feel very "legendary" since monsters keep sporting ever-higher Armor Classes, and you don't really feel like you're ever getting to dominate the game.
The answer of course is that "legendary" is just a label. The point in this game is that you remain 2 points ahead of the other heroes.
But of course I understand his sentiment - there's nothing "legendary" by a +10% boost.
I have a similar issue with PF2 (and modern systems in general), but it’s the opposite side of that same coin. I look at it this way. If you’re balancing challenges out to an appropriate level of difficulty, then all you’ve done is recreate the experience of those percentile tables from old-school D&D with a lot more indirection. Bleh. Fie to that.
This downplays the importance of showing how the game can be played too much for my liking.
It kind of goes both ways when official adventures get trotted out in a discussion regarding other ways of playing the game.
We can of course discuss whether PF2's design is specifically and precisely geared towards the exact playstyle showcased by the official material, but I hope we agree Pathfinder 2 is - like every other game - better equipped to handle some campaign styles than others.
I'm just saying that I find it natural to claim PF2 isn't created for sandbox play. Can it be used for such a campaign? Yes of course, but the question really asks if the game in question really is an easy and straightforward choice of ruleset?
In PF2's case, I'd say you need to tweak so many things you're probably better off using another engine to start with. Again it's not that it can't be done, but why do a lot of work when other games let you get away with a little?
“Sandbox” often gets taken to mean some kind of *crawl, but it’s a bit broader than that. A sandbox is a game where the PCs make decisions, and what happens next follows from the consequences of those decisions. Basically, you generally start with a world in a status quo, and then you inject the PCs.
I’d argue that an adventure like
Winter’s Daughter is a sandbox because it doesn’t prescribe any particular narrative direction. Aside from the hook serving as a default action for the PCs, it doesn’t prescribe any particular outcome. Due to how it’s structured,
something will come of it, but what exactly is left open (to be answered by playing through the adventure).
If that seems like a stretch, consider a campaign where the PCs arrive in town. There are several in proximity, and they all have problems needing to be solved. As time goes by, the problems will get worse. As they solve problems, they’ll get stronger by nature of not having been solved quickly enough. This still isn’t a crawl, but it’s a sandbox because how and what gets solved comes down to the decisions the PCs make.
I mention “getting worse” just as a way to keep things in step with PF2’s default power curve. For example, one town has problems with bandits. The town is especially worried because they’ve seen an ogre with the bandits. Eventually, if nothing is done, the ogre will call for help from other ogres, and the ogres will take over the bandits, and now you have a bunch of marauding ogres threatening the town. The bandits aren’t all killed by the ogres, so now they’re potentially a faction you can enlist to help fight the ogres, but the town’s not going to like that. What do you do?
How all that gets solved comes down to what approach the PCs take. That’s if they even bother. They could prefer hanging out in the dragon hotsprings or going after undead instead. As a rule of thumb, if you could run two parties through the same scenario and get wildly different results (differing beyond the details), then you might have a sandbox.
As for a traditional *crawl, I think you can do it as long as you use Proficiency Without Level. The reason isn’t to make higher level monsters easier but to allow lower level ones to stay relevant longer. If you’re just setting up a map for PCs to explore, they’ll eventually get more powerful, and dealing with new areas that were created with lower-level threats would feel boring if those threats aren’t worth anything. However, it might be possible to to keep the standard power curve and emphasize henchman and sidekicks as a way of keeping those lower level areas interesting.
Anyway, if the claim is that PF2 doesn’t have a lot to say on running a sandbox or provide tools for that, then that’s true, but that’s true of 5e and most other modern systems. You end up having to lean pretty heavily on techniques shared by GMs because that stuff just doesn’t get put in books anymore. I can’t comment on older ones that did (beyond my familiarity with OSE), but I expect there wasn’t much more than the procedure to go by (so no advice either).
Not exactly sure what you mean by set pieces?
If you mean a focus on extra-special combats, where extra care has been taken to challenge the players (maybe special terrain or particular interactions between the monsters or tasks the characters have to perform while fighting) then no, there aren't really any set pieces.
If you merely mean that (nearly) every fight is intended to be challenging in itself, then yes, very much so. Everything about the game is geared towards forgetting about resources and making the individual fight the centerpiece of today's excitement.
So when you contrast to 4E, then I think I know what you mean (and agree).
I’d say yes to “extra-special” but not necessarily to focusing on challenge. I think a set piece battle focuses more on creating dramatic moments and setting up the PCs to do cool things. If you have a swashbuckler, then there will be chandeliers to swing from. That kind of thing.
I guess I'm getting bored with the ultra-sharp focus on encounter balance. Everything about the game and the adventures suggest it would be a shame if the players were to do something smart that shortcircuits the fight (its challenge level) - that a fight where the lethality has been defused is a waste, but I don't agree. I think things become more interesting and engaging if the players realize they are allowed to make smart story decisions that are rewarded by pushover fights (=less risk of death).
I’d suggest just ignoring whatever is suggesting that and let the PCs be smart and get their advantage. It may “break” the adventure, but that doesn’t really matter as long as everyone is having fun.